1. Field of the Invention
The present invention relates to a system and method for providing a congestion optimized address resolution protocol for wireless ad-hoc networks. More particularly, the present invention relates to a system and method for enabling a node on a wireless ad-hoc network to issue an address resolution protocol request without the need to broadcast the request to a plurality of other nodes on the wireless ad-hoc network, to thus minimize the amount of traffic on the network necessary to handle the request.
2. Description of the Related Art
In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed for use by the military. In this type of network, each user terminal is capable of operating as a base station or router for the other user terminals, thus eliminating the need for a fixed infrastructure of base stations. Details of an ad-hoc network are set forth in U.S. Pat. No. 5,943,322 to Mayor, the entire content of which is incorporated herein by reference.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling user terminals to communicate with each other as in a conventional ad-hoc network, further enable user terminals, also referred to as subscriber devices, to access a fixed network and thus communicate with other user terminals, such as those on the public switched telephone network (PSTN), and on other networks such as a local area network (LAN) and the Internet. Details of these types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, filed on Jun. 29, 2001, and in U.S. patent application Ser. No. 09/815,157 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel”, filed on Mar. 22, 2001, the entire content of both of said patent applications being incorporated herein by reference.
Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol address (IP address) to a physical machine address that is recognized in a local network, such as a LAN. For example, in IP Version 4, which is the most common level of IP in use today, an address is 32 bits long. In an Ethernet local area network, however, addresses for attached devices are 48 bits long. The physical machine address is also commonly referred to as a Media Access Control or MAC address. A table, usually called the ARP cache, is used to maintain a correlation between each MAC address and its corresponding IP address. ARP provides the protocol rules for making this correlation and providing address conversion in both directions, that is, from IP address to MAC address and vice-versa.
ARP functions in the following manner. When an incoming packet destined for a host machine on a particular LAN arrives at a gateway on the LAN, the gateway requests that the ARP program find a physical host or MAC address that matches the IP address. The ARP program looks in the ARP cache at the gateway and, if it finds the MAC address, provides the MAC address so that the packet can be converted and formatted as appropriate and sent to the machine. If no entry is found for the IP address in the ARP cache, the ARP program broadcasts a request packet in a special format to all the machines on the LAN to see if any machine recognizes that IP address as being associated with its MAC address. A machine that recognizes the IP address as its own returns an affirmative reply to the ARP program. A machine configured to respond to requests for an IP addresses other than its own, for which it is said to proxy, returns an affirmative reply if it recognizes the IP address as one for which it is so configured. In response, the ARP program updates the ARP cache for future reference, and then sends the packet to the machine having the MAC address associated with the IP address for which the packet is intended. Examples of conventional ARP techniques performed in asynchronous transfer mode (ATM) networks employing LANs are described in a publication by M. Laubach and J Halpern entitled “Classical IP and ARP over ATM”, IETF RFC 2225, April, 1998, in a publication by Jill Kaufman entitled “ATM Forum Education Corner”, ATM Forum, 2001, and in a publication by Rajeev Gupta entitled “The ‘Glue’ of Networks: Looking at IP over ATM”, ATM Forum, 2001, the entire contents of each of these documents is incorporated herein by reference.
Although the process described above is suitable for use with wired networks and broadcast wireless, the process is not suitable for use in an ad-hoc wireless network. Specifically, in an ad-hoc wireless network, when the ARP of a node causes a broadcast of the ARP request packet to all the nodes on the wireless network, such a broadcast could flood the radio network since it would be required to be repeated by every node to ensure completeness.
The MANET working group within the IETF is evaluating techniques in which to accomplish the delivery of such broadcast messages from a node in a wireless LAN. For example, the message can be via a broadcast of the IP address to all nodes on the network, or via a single hop broadcast to only neighboring nodes. In the case in which the message is broadcast to all nodes on the network, the amount of radio traffic generated on the network is enormous because each node must insure that its neighbors receive the message. Although certain techniques can be used to reduce this overhead, there is no mechanism for delivering a broadcast message toward a destination capable of resolving the ARP. Alternatively, in the single hop case, a node which is not directly connected to a node which can resolve the ARP request will never receive a reply. In addition, in either case, the reliability of the broadcast transfer can be severely impacted by the hidden terminal problem common in ad-hoc networks, as well as the near/far problem in which a node near to a node receiving a signal from a more distant node inadvertently transmits to the near node and thus destroys the ongoing reception from the distant node. A hidden terminal is a node which is out of range of a transmitting node and can therefore destroy an ongoing reception. This effect is particularly detrimental to broadcast transmissions which do not require a clear-to-send operation by the receiving node. Without the clear to send, the hidden terminal has no knowledge that a transmission is occurring and is free to attempt a transmission. An example of a non-broadcast multi-access subnetwork (NBMA) is described in a publication by J. Luciani et al. entitled “NBMA Next Hop Resolution Protocol (NHRP)”, IETF RFC 2332, April 1998, the entire contents of which is incorporated herein by reference.
Accordingly, a need exists for a system and method for improving the manner in which ARP is performed on wireless ad-hoc networks.